1. Field Of The Invention
These inventions generally relate to plasma caused by a microwave source, and more particularly, to apparatus and processes for detoxification of hazardous wastes by use of microwave plasma.
2. Description of The Art
A microwave plasma provides rapid "in-situ" detoxification of liquid and gaseous hazardous wastes. This was substantiated by the Lockheed Palo Alto Research Laboratory, as published in DEVELOPMENT OF MICROWAVE PLASMA DETOXIFICATION PROCESS FOR HAZARDOUS WASTE PHASE III, under EPA(SHWRD) Contact No. 68-03-2190 by project officer D. A. Oberacker. The objective of that PHASE III program was to assemble a 15 kilo-Watt microwave plasma (1.45 liter) reactor capable of destroying two to eleven kilo-grams (five to twenty-five pounds per hour) of hazardous wastes, and to determine the destruction efficiencies for various types of waste, i.e., sampling and analysis system to determine trace amounts of any reactants leaving the plasma reactor. Achieved destruction efficiencies were greater than 99.98 to 99.9998 per cent. Efficiency and other than laboratory capacity will depend upon further efforts to improve the reactor design.
Current efforts toward reactor design, albeit for other applications, are represented by Asmussen, et al, U.S. Pat. No. 4,727,293 and Pichot, et al., U.S. Pat. No. 4,745,337, provide a microwave-driven ion generator, but rely upon a plurality of permanent magnets. The elevated temperatures associated with a plasma are not believed to enhance either the performance or longevity of the permanent magnets. Other efforts such as those of Consoli, et al, U.S. Pat. No. 3,774,001, Hull,, et al., U.S. Pat. No. 4,766,351, and Muller, U.S. Pat. No. 4,849,675, rely upon induction heating to generate a plasma.
One earlier effort, by Kirjushin, U.S. Pat. No. 3,577,207 describes a low-temperature plasma generator constructed with a gas-discharge region enclosed in a cylindrical tube symmetrically positioned along an axis of a spherical or cylindrical microwave cavity resonator. The cavity resonator is driven by microwave energy from an equatorially positioned waveguide coupled to the cavity via a plurality of slots in the wall of the cavity, which are equidistantly spaced from the longitudinal axis of the gas discharge tube. Holes in the wall of the cavity through which the gas discharge tube passes are fitted with stubs having diameters less than the critical dimension, to prevent emission of microwave energy to the outside of the cavity, while a turbulent jet of plasma-forming gas is said to keep the plasma from touching the walls of the gas discharge tube. In effect, Kirjushin '207 discloses a plasmatron.
Like Kirjushin '207, other earlier efforts such as Weissfloch, et al., U.S. Pat. No. 3,814,983, and some current efforts such as Mosian, et al., U.S. Pat. No. 4,049,940, Bloyet, et al., U.S. Pat. No. 4,473,736, and Moisan, et al., U.S. Pat. No. 4,810,933, have used cylindrical gas columns or tubes making a single pass through a microwave field as plasma vessels, while other current efforts, such as shown by Sugawara, U.S. Pat. No. 4,735,764, and by Lee, et al., U.S. Pat. No. 4,716,340, use a single chamber driven by a microwave source to create a localized plasma.